This application claims the benefit of Japanese Patent applications Nos. 2000-063984 and 2000-127242 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a light path deviation detecting apparatus for detecting deviations (shift and tilt) of a detection target light path, and to a confocal microscope mounted with this light path deviation detecting apparatus.
2. Related Background Art
A confocal microscope is superior to a general microscope in terms of its resolution and other various performances, and is used widely in industrial and biological fields.
FIG. 7 is a diagram showing a laser scan type confocal microscope as this type of confocal microscope.
Referring to FIG. 7, a light source 11 emits linearly polarized laser beams. A beam expander 12 expands a beam diameter of the laser beam. The laser beam with the expanded beam diameter travels straight through a polarized beam splitter 13 and reaches a xc2xc wavelength plate. The xc2xc wavelength plate 14 transforms the laser beam into circularly polarized light and emits the same polarized light to a scan unit 15.
This scan unit 15 scans the laser beam in two-dimensional directions by use of a biaxial mirror drive mechanism. An objective lens 18 converges the scan light at an observation point on a sample 19.
The scan light reflected by the sample 19 becomes reversely circularly polarized light. The reversely circularly polarized light travels tracing back the objective lens 18 and the scan unit 15, and arrives at the xc2xc wavelength plate 14.
The xc2xc wavelength plate 14 transforms the circularly polarized light into rectilinearly polarized light of which the polarizing direction is orthogonal to the direction when illuminating, and emits the linearly polarized light to the polarized beam splitter 13. The polarized beam splitter 13 reflects the linearly polarized light. A condenser lens 21 converges the reflected linearly polarized light at a pinhole 23 of a light shielding plate 22. A photoelectric detecting device 24 receives the light penetrating this pinhole 23.
An A/D converter 25 converts an output of luminance of the photoelectric detecting device 24 into a digital signal.
A CPU 26 takes in the digital signal from the A/D converter 25 with a sampling clock synchronizing with the scan operation of the scan unit 15, and generates an image of the sample 19. This image is properly displayed on a display 27.
By the way, in this type of confocal microscope, an exit position and an exit angle of the laser beam fluctuates due to a change in characteristic of the light source and to a positional change of the internal optical element when switching a wavelength (in the case of the light source capable of switching the wavelength such as a titanium/sapphire laser).
FIG. 8A is a diagram showing a state drawn by a dotted line, wherein a shift occurs on the light path of the light source 11 for the reason given above. If such a shift occurs, the laser beam for the illumination deviates from a range of an entrance pupil 17 of an objective lens 18. As a result, a quantity of the illumination light upon the sample 19 decreases, resulting in an inconvenience such as a decrease in S/N ratio of the sample image.
Further, FIG. 8B shows a state indicated by a dotted line, wherein a tilt occurs in the light path of the light source 11. If such a tilt occurs, an illumination point on the sample 19 shifts. As a result, an observation point on the sample, which is in an optical conjugate relationship with the pinhole 23, is not sufficiently illuminated with the laser beam. Further, in the worst case, the converging position completely deviates from the pinhole 23 with the result that no image is obtained.
The prior art confocal microscope does not include a device for detecting the exit position and the exit angle of the laser beam. Therefore, the operator often continues to use the confocal microscope while being unaware of the above inconvenience. Further, the operator, even if aware of the inconvenience described above, must request a service center for maintenance each time because of providing no contrivance for precisely calibrating the light path deviation.
Moreover, some of the confocal microscopes have a plurality of light sources. In this type of confocal microscope having the plurality of light sources, it is difficult and intricate to adjust the laser beams of each light source exactly onto the same optical axis.
It is a primary object of the present invention, which was devised under such circumstances, to provide a light path deviation detecting apparatus capable of detecting light path deviation categorized distinctively into a shift or a tilt.
It is another object of the present invention to provide a light path deviation detecting apparatus capable of enhancing an accuracy of detecting the light path deviation by effectively reducing stray light generated inside.
It is still another object of the present invention to provide a confocal microscope capable of detecting light path deviations categorized distinctively into a shift or a tilt.
It is a further object of the present invention to provide a confocal microscope capable of automating correction of a deviation of an illumination light path.
It is still a further object of the present invention to provide a confocal microscope capable of easily executing calibrating the light paths of a plurality of light sources.
The light path deviation detecting apparatus and the confocal microscope, which accomplishes the above object, will hereinafter be described in a way of giving the corresponding components the same numerals as those in the embodiment. Note that the corresponding components are given herein for reference but do not any limitation to the present invention.
According to a first aspect of the present invention, as shown in FIG. 1, a light path deviation detecting apparatus for detecting a deviation of a detection target light path (which may be a light path deviation between, e.g., a fiducial light path and the detection target light path), comprises a diverging element (51, 52) for diverging the detection target light path into at least two light paths, and light detecting devices (53, 54, 55, 26), of which light receiving surfaces are disposed spaced light path lengths different from each other from respective diverging destinations of the diverging means, for detecting respectively light receiving positions on the light receiving surfaces. The light detecting devices detect a tilt of the detection target light path from a difference between the light receiving positions detected respectively by the light detecting devices.
FIG. 9 shows one example, wherein the light receiving surfaces of the light detecting devices are disposed spaced light path lengths different from each other from the respective diverging destinations. FIGS. 10A and 10B imaginarily show a state where the light receiving surfaces A, B shown in FIG. 9 are disposed equally on the detection target light path. The principle on the above geometry will hereinafter be explained by use of the imaginary light path shown in FIGS. 10A and 10B.
Referring first to FIG. 10A, a tilt (with an elevation angle xcex8, and a rotational angle "psgr") occurs in the detection target light. This beam of detection target light reaches at first a light receiving position Pa of the light receiving surface A. Thereafter, the detection target light travels forward only a light path length difference xcex94L in the direction (defined by the elevation angle xcex8 and the rotary angle "psgr"), and arrives at a light receiving position Pb of the light receiving surface B.
Therefore, a deviation width between the two light receiving positions Pa and Pb is equal to (xcex94Lxc2x7tan xcex8). The light path length difference xcex94L of these parameters is already known, and hence the elevation angle xcex8 of the tilt can be obtained from the deviation width between the light receiving positions Pa and Pb. Further, the rotational angle "psgr" can be obtained directly from an inclined direction of the deviation.
Thus, the tilt of the detection target light path can be surely detected based on the difference between the light receiving positions of the respective diverging destinations. Further, the angle of the detection target light is adjusted so as to eliminate the difference between the light receiving positions (so that the light receiving positions may become coincident), thereby making it possible to correct the tilt of the detection target light.
On the other hand, referring to FIG. 10B, only a shift S occurs in the detection target light. The detection target light reaches at first the light receiving position Pa of the light receiving surface A. Thereafter, the detection target light travels in parallel with a reference optical axis, and arrives at the light receiving position PB of the light receiving surface B. In this case, the two light receiving positions Pa, Pb become coincident enough to cause no deviation. At this time, the shift S can be obtained directly from an absolute position of the light receiving position Pa (Pb). Further, the position of the detection target light is adjusted so that the light receiving position becomes coincident with an origin, whereby the shift of the detection target light can be also corrected.
According to a second aspect of the present invention, as shown in FIG. 3, a light path deviation detecting apparatus for detecting a deviation of a detection target light path, comprises diverging means (51, 52) for diverging the detection target light path into at least two light paths, light detecting devices (53, 54, 55, 26), of which light receiving surfaces are disposed at respective diverging destinations of the diverging means, for detecting respectively light receiving positions on the light receiving surfaces, and a light converging element (71), disposed at at least one diverging destination of the diverging means, for converging parallel beams of light with no occurrence of tilt at a predetermined position on the light receiving surface, wherein a tilt of the detection target light path is detected from a deviation of the light receiving position at the diverging destination provided with the light converging means from the predetermined position.
The principle of the above geometry will hereinafter be described with reference to FIGS. 11 and 12.
Referring first to FIG. 11, the tilt does not occur in the detection target light, and only the shift occurs. This sort of detection target light, of which the light path is deflected by the light converging element 2, reaches a predetermined position X on a light receiving surface Q. If a light receiving position P of the detection target light is thus coincident with the predetermined position X, it can be judged that the tilt does not occur in the detection target light.
While on the other hand, referring to FIG. 12, the tilt (defined by the elevation angle xcex8 and the rotational angle "psgr") occurs in the detection target light traveling through the light converging element 2. The detection target light arrives at a light receiving position Pxe2x80x2 on the light receiving surface Q regardless of the shift. A deviation width of this light receiving position Pxe2x80x2 from the predetermined position X is equal to F1xc2x7tan xcex8. F1 of these parameters corresponds to a distance (focal length) between a back or secondary principal point H of the light converging element and the light receiving surface Q, and is already known. Accordingly, the elevation angle xcex8 of the tilt can be obtained from a value of this deviation width. Further, the rotational angle "psgr" can be obtained directly from the inclined angle of the deviation. The symbol H in FIG. 12 indicates the back or secondary principal point.
Thus, the tilt of the detection target light path can be surely detected based on the deviation of the light receiving position from the predetermined position. Further, the angle of the detection target light is adjusted so as to eliminate this deviation (so that the light receiving position may become coincident with the predetermined position), whereby the tilt of the detection target light can be also corrected. In this case, the predetermined position with which the light receiving position should be made coincident is a fixed point, and hence an advantage is that the correcting operation is more facilitated than in the first aspect of the present invention.
Moreover, the thus detected tilt is removed from the light receiving position at the other diverging destination, whereby the shift of the detection target light path can be also detected.
According to a third aspect of the present invention, as shown in FIGS. 13 and 14, in the light path deviation detecting apparatus according to the first or second aspect, the diverging means may include a stray light hindering device (112, 113, 118, 119) for hindering at least a part of stray light caused in the diverging means from reaching the light receiving surface of the light detecting device.
In the light path deviation detecting apparatus, the stray light might be generated when taking the light out of the detection target light path. The thus generated stray light reaches the light receiving surface at the diverging destination, wherein a false spot image 103 is formed (see FIG. 15a). If the false spot image 103 is formed, a centrobaric position 102 of a light distribution on the light receiving surface shifts, and therefore the light detecting device judges this centrobaric position 102 as an apparent spot image, and mis-detects the light receiving position. As a result, an accuracy of the light path deviation detecting apparatus declines.
By the way, if the type of the light source used herein is singular and this light source is fixed, the shift of the centrobaric position is constant each time, and hence the light detecting device is capable of comparatively easily correcting the shift of the light receiving position.
If the plurality of light sources are exchangeably used, however, an intensity ratio of normal light to the stray light and the position change due to slight differences between the layout positions of the light sources, between the wavelengths and between the polarizing directions, with the result that the centrobaric position of the light distribution on the light receiving surface shifts complicatedly. Therefore, the optical apparatus using exchangeably the plurality of light sources is quite difficult to precisely correct the shift of the light receiving position.
Such being the case, according to the geometry described above, the stray light hindering device is provided for hindering at least a part of the stray light from reaching the light receiving surface of the light detecting device. As a consequence, the influence of the false spot image disappears, and the accuracy of detecting the light path deviation can be exactly enhanced.
According to a fourth aspect of the present invention, in the light path deviation detecting apparatus according to the third aspect, the diverging means is a half-mirror obliquely provided on the detection target light path, and the stray reflected light hindering device includes an incidence restricting member (112) for hindering stray reflected light occurred in the half-mirror from entering a passing range of normal reflected light by restricting a passing range of incident light upon the half-mirror, and a reflection restricting member (113) for hindering the stray reflected light occurred in the half-mirror by restricting a passing range of the reflected light from the half-mirror.
According to this configuration, the incidence hindering member restricts the incidence range of the half-mirror, thereby hindering the stray reflected light from entering the passing light path of the normal reflected light. On the other hand, the reflection restricting member hinders directly the stray reflected light occurred by the half-mirror.
Accordingly, the stray reflected light can be certainly hindered on both of the incident and reflecting sides of the half-mirror.
According to a fifth aspect of the present invention, in the light path deviation detecting apparatus according to the third aspect, the diverging means is a half-mirror obliquely provided on the detection target light path, and the stray reflected light hindering device is constructed of a light shielding mask (118, 119) for masking the half-mirror, and has a front surface performing a function of hindering the stray reflected light occurred in the half-mirror from entering the passing range of the normal reflected light by restricting the passing range of the incident light upon the half-mirror, and a rear surface performing a function of hindering the stray reflected light occurred in the half-mirror by restricting the passing range of the reflected light from the half-mirror.
According to this configuration, the front surface of the light shielding mask functions to restrict the incidence range of the half-mirror. On the other hand, the rear surface (facing to the half-mirror) of the light shielding mask functions to restrict directly the stray reflected light occurred by the half-mirror. Accordingly, the stray reflected light can be certainly hindered on both of the incident and reflecting sides of the half-mirror.
According to a sixth aspect of the present invention, in the light path deviation detecting apparatus according to the fourth or fifth aspect, the stray reflected light hindering device sets a passing boundary of the reflected light in a xe2x80x9clight path deviation between the normal reflected light and the stray reflected lightxe2x80x9d that occurs due to a thickness and a refractive index of the half-mirror. The beam of light entering the half-mirror is reflected by the two portions, i.e., the front surface and the rear surface of the half-mirror. One beam of light (normally exhibiting a larger light intensity)of these reflected beams of light turns out to be the normal reflected light, and the other becomes the stray reflected light. Therefore, a light path deviation with a fixed width proportional to the thickness of the half-mirror occurs between the normal reflected light and the stray reflected light. Then, the stray reflected light hindering device sets the boundary of the passing range of the reflected light within this light path deviation, thereby making is possible to selectively hinder the stray reflected light.
According to a seventh aspect of the present invention, as shown in FIG. 5, a confocal microscope comprises a light source (11) for illumination, an illumination optical system (12, 13, 14, 18) for irradiating a sample with the light from the light source, an observation optical system (13, 14, 18, 21) for converging the light reflected from the sample, a pinhole (23) disposed in an optical conjugate position through the observation optical system to an observation point on the sample, a scanning unit (15) for optically scanning the observation point over the sample, a light receiving element (24) for receiving the light penetrating the pinhole, and image forming unit (26) for forming an image of the sample from a relationship between a light intensity obtained from the light receiving element and the scanning operation of the scanning unit. The light path deviation detecting apparatus according to the first or second aspect is provided on an illumination light path of the illumination optical system and thus becomes capable of detecting a shift and a tilt of the illumination light path.
According to this architecture, the light path deviation detecting apparatus according to the first or second aspect is provided on the illumination light path of the confocal microscope. The deviation of this illumination light path leads to large declines of an image resolution and an image quality. Accordingly, this illumination light path is provided with the light path deviation detecting apparatus, whereby a decline of performance of the confocal microscope can be quickly surely detected. Further, it is also feasible to accurately easily execute a calibrating operation of the confocal microscope.
According to an eighth aspect of the present invention, as shown in FIG. 5, the confocal microscope according to the seventh aspect may further comprise a tilt control device (26, 81, 82, 85) for automatically correcting the tilt of the illumination light path by turning the illumination light path corresponding to the tilt of the illumination light path that is detected by the light path deviation detecting apparatus, and a shift control device (26, 83, 84) for automatically correcting the shift of the illumination light path by moving the illumination light path in parallel corresponding to the shift of the illumination light path that is detected by the light path deviation detecting apparatus.
According to this configuration, the confocal microscope is provided with the tilt control device and the shift control device. These control devices automatically correct the tilt and shift of the illumination light path on the basis of the result of detection of the light path deviation detecting apparatus. The deviation of the illumination light path is thus automatically corrected, thereby actualizing the highly reliable confocal microscope exhibiting a variety of stabilized performances such as the image resolution and the image quality.
According to a ninth aspect of the present invention, in the confocal microscope according to the seventh aspect, the light source includes plural types of selectable light sources (91, 92, 93), and the light path deviation detecting apparatus is disposed on the illumination light path common to the plural types of light sources, and has a calibrating device (100) capable of calibrating a light path deviation between the plural types of light sources while referring to a result of detection of the light path deviation detecting apparatus. In this confocal microscope, the light path deviation detecting apparatus is disposed on the illumination light path common to the plurality of light sources. Accordingly, the single unit of light path deviation detecting apparatus is capable of detecting the light path deviation with respect to the plurality of light sources.